The present invention relates to a signal break detecting circuit and particularly to a signal break detecting circuit for detecting a signal break in optical signals received by an optical receiving unit.
If a break occurs in optical signals received by an optical receiving unit or a fiber is disconnected or in case of wave length division multiplex (WDM), an optical fiber amplifier (OFA) gets in trouble, such a transmission path failure is detected and alarm (loss of signal) is dispatched. This function is an indispensable function specified according to international telecommunications union (ITU) for distinguishing such transmission path failure from unit failure.
When this alarm is dispatched, the optical receiving unit confirms operation of a mating unit and gets into a sequence for switching the transmission path to a reserved system (These are specified according to TMN of ITU-T and controlled by network control system of each unit). If all failures are vanished, the network control system confirms with the mating unit and switches back from the reserved system to its current system.
Because basically, the alarm acts as a trigger for executing automatic switching with the mating unit (mating units between different companies are considered), certainty and dispatch time are considered important. Although the alarm dispatch time is not specified according to ITU especially, the alarm is requested to be dispatched in 2.3 xcexcsxcx9c100 xcexcs according to the specification of Bellcore. That is, considering switch-over with cross connection or same sign continuity (for example, for distinguishing whether data having continuous xe2x80x9c0xe2x80x9d level is received or the xe2x80x9c0xe2x80x9d level is attained due to signal break), it is requested that respective rates of synchronous optical network (SONET) do not dispatch any alarm within 2.3 xcexcs since data signal break.
On the other hand, the data signal break in a conventional optical receiving unit is detected by detecting that a peak value of reception signal drops to a predetermined value. Further, technology for detecting the signal break using timing signal extracted from the reception signal has been disclosed in each of Japanese Patent Application Laid-Open No. 5-260032 (hereinafter referred to preceding technical document 1), Japanese Patent Application Laid-Open No. 3-79141 (hereinafter referred to as preceding technical document 2) and Japanese Patent No. 3045069 (hereinafter referred to as preceding technical document 3).
However, the conventional optical receiving unit has such a disadvantage that it takes a long time until data signal break is detected since that break occurs, because it detects that the peak value of the reception signal drops to a predetermined value. On the other hand, any means which solves this disadvantage has not been disclosed in the preceding technical documents 1-3.
Accordingly, an object of the present invention is to provide a signal break detecting circuit capable of reducing time necessary for detecting a data signal break as compared to the conventional detecting circuit.
To achieve the above object, the present invention provides a signal break detecting circuit for detecting a signal break in reception signal, comprising: a first value detecting means for detecting a first value obtained corresponding to the amplitude of the reception signal; a second value detecting means for detecting a second value which is obtained corresponding to the amplitude of the reception signal and different from the first value; a difference detecting means for detecting a difference between the first value and the second value; and a comparing means which compares output of the difference detecting means with a predetermined reference value and outputs a comparison result.
According to the present invention, by comparing a difference between the first value and the second value obtained corresponding to the amplitude of the reception signal, signal break is detected. Consequently, time necessary for detecting the data signal break can be reduced, as compared to the conventional detecting circuit.
The present invention achieves a signal break detecting circuit for detecting a signal break in reception signal, comprising: a first value detecting means for detecting a first value obtained corresponding to the amplitude of the reception signal; a second value detecting means for detecting a second value which is obtained corresponding to the amplitude of the reception signal and different from the first value; a difference detecting means for detecting a difference between the first value and the second value; and a comparing means which compares output of the difference detecting means with a predetermined reference value and outputs a comparison result. Consequently, time necessary for detecting data signal break can be reduced.